1. Field of the Invention
The present invention relates to a static pose fixture that is utilized in motion capture systems. More specifically, the present invention relates to a static pose fixture utilized to measure geometry and body plate marker locations of a subject for preparation of a motion capture model during a golf swing.
2. Description of the Related Art
Motion Capture is used to measure the position and or orientation of any object, usually at multiple points in time. There are four main categories of motion capture devices, mechanical, magnetic, passive optical, and active optical. An example of a mechanical device is the Cyberglove®. A mechanical device measures the orientation of rigid links mounted to a subject. A magnetic device such as the Ascension MotionStar® or Polhemus StarTrak® measures the position and orientation of wire coils attached to the subject. Since golf clubs are typically constructed of metal or metal parts, magnetic systems, which may loose accuracy when metal objects are near by, may experience some distortion during a golf swing motion measurement. Passive optical systems use multiple cameras to triangulate the position of reflective markers placed on the subject. Exemplary examples of a passive optical system are those made by Vicon and Motion Analysis. Active optical systems use triangulation to track the position of infrared light emitting diodes. Exemplary examples of active optical systems include systems such as Northern Digital's Optotrak and Charnwood Dynamics CODA. Active optical systems have the ability to distinguish markers from one another, which greatly decreases the time it takes to process data and which makes them a preferred device for use with the static pose fixture as described herein, however, any of the devices as previously discussed may be used.
An active optical motion device is able to determine the position and orientation of a rigid object as long as 3 non co-linear markers on that object are in view of the sensors. An occluded marker is a marker that is not in view of any of the sensors. One marker on a rigid body plate is selected to be the origin of a coordinate system. The 3D position of each marker on the plate is measured, and the position and orientation of the plate is then reported with respect to the global origin. To generate the best possible motion capture data, it is important to have more than 3 non co-linear markers on each rigid body to increase the chances that at least three markers on the body are not occluded, since the object itself can come between a marker and a sensor.
To drive a computer generated human model with motion capture, data markers of any type (retro-reflective, active IRED, magnetic, etc.), are mounted on the subject in areas where the motion must be acquired. The subject is then asked to stand straight with arms in a horizontal position, thus forming a cross with the body. A frame of data is acquired in the form of a point cloud. Within the software, the operator then moves the human model into the point cloud so that each marker is near the same location within the model as on the subject. If the subject has not assumed the exact same posture as the default posture of the model, the operator rotates the limbs to mimic the subject's posture. If the subject is a different size compared to the model, the operator lengthens or shortens each limb so that it looks correct. Once the model is sized and oriented properly within the point cloud, the configuration is saved and any further motion data acquired from the subject can be used to drive the motion of the model. Some human modeling software allows the user to measure body segments and input values, which can increase accuracy but is relatively time consuming.
Several methods of capturing motion data have been proposed including Nesbit et al., U.S. Pat. No. 5,772,522, which discloses the analysis and measurement of a representative model during an active motion such as a golf swing.
Further examples include Kramer, U.S. Pat. Nos. 5,592,401 and 6,148,280, which disclose the use of sensor devices placed on a subject during an active motion, like a golf swing, thereby enabling the capture and analysis of the motion.
Still more examples include Haas et al., U.S. Pat. No. 4,137,566, which discloses the use of a plurality of reflective sources and a data collector to record active motions, like golf swings, for analysis. Mann, U.S. Pat. No. 4,891,748, discloses using video images in preparation of computer generated models.
However, the process of sizing and orienting the model in the point cloud is time consuming and inaccurate. Because the orientation of each limb in space is estimated by the operator, it is subject to variation and inaccuracy. If it is assumed that the subject is standing with arms perfectly horizontal when the arms are actually skewed slightly or bent, the location of markers on the wrists of the subject will be modeled with a high degree of inaccuracy. As motion capture data is used to drive the model, this inaccuracy will cause the wrist to be driven to a location that is offset from the measured location. When modeling a golf swing, even slight inaccuracy in the wrists can lead to large inaccuracy in the location of the club head, rendering the model far less useful. Additionally, if any of the markers move with respect to the subject once the model generation is complete, the process must be repeated from the beginning or further inaccuracy will result.